Various storage devices utilizing a storage tiering technique, so-called tiered block storage devices, have recently been developed. The storage tiering technique ties together the physical storage areas (hereinafter, referred to as physical volumes) of various types of storage devices of different access response performances. As a result, the storage tiering technique constructs at least one virtual storage area (hereinafter, referred to as a logical volume) including a plurality of physical volumes as entities. The logical volume is also called a logical disk and can be recognized by a host device (computer).
In the storage tiering technique, a set of storage devices (physical volumes) of the same type is called “a tier.” In general, storage devices of higher access response performances are allocated (positioned) to a higher-tier. Namely, the tiered block storage device is provided with various types of storage devices of different tiers, and the logical disk is formed using the physical volumes of the storage devices of different tiers.
In a computer system having the tiered block storage device, it is requested to locate a designated file in a designated tier. In general, the tiered block storage device cannot recognize a file. In view of this, in the prior art, a special file system (file system program) is provided in the tiered block storage device. This special file system associates a file used by the host device with positions on the logical disk of blocks constituting the designated file. As a result, the tiered block storage device (more specifically, the storage controller of the tiered block storage device) can specify blocks that constitute the designated file and can locate them in the designated tier.
As mentioned above, in the prior art, a function of locating a designated file in a designated tier is realized by a special file system provided in the tiered block storage device. Namely, the conventional tiered block storage device requires the special file system.